LED display devices including LEDs are widely used to display, for example, indoor and outdoor advertisements. These LED display devices have been used as large-sized display devices having pixel pitches of 3 mm or larger, however, in recent years, the LED display devices have reduced cost and narrowed pixel pitches of the LEDs, thus have been brought to market as products having pixel pitches of 1.5 mm and 1.9 mm.
In accordance with the narrowed pixel pitch, the LED constituting one pixel is made up of an extremely small package having a size of 1.0 mm×1.0 mm or smaller. The reduction in the size of the package causes a decrease in a yield in a soldering process due to a reduction in an area of a soldering pad depending on a total number of terminals, and also causes a trouble such as an increase in cost due to a complicated pattern and an increased number of layers in a substrate. Widely used as a method of solving these problems is a package of an anode common in which anodes of the LEDs in red, green, and blue are electrically connected so that a minimal number of terminals are included in the package.
However, a voltage supplied to each of the LEDs in red, green, and blue is common in the anode common, so that when a forward voltage of each LED differs from each other, an electrical power is wastefully consumed in accordance with the difference in the forward voltage, thus a defect such as an increase in the consumed power occurs. When the consumed power increases, an amount of heat generation also increases, thus a defect such as a decrease in a lifetime of the LED due to an increased temperature of LED itself also occurs. Accordingly, proposed is a method of driving a cathode common in which cathodes of the LEDs are electrically connected to achieve a reduction in the consumed power in the LED and a long lifetime of the LED (for example, Patent Document 1).